This invention relates to gelling clays and, more particularly, to a method of treating normally nongelling clays so that they may be used as gelling agents for thickening aqueous and organic liquid systems.
Certain clay mineral products are known as gelling clays. Such clays are used for thickening drilling muds, liquid animal feeds, suspension fertilizers, asphalt cutbacks and oil base foundry sand binders, and are also used for stabilizing coal/oil mixtures.
Typical gelling clays include Wyoming bentonite, attapulgite, sepiolite, and hectorite. These gelling clays can be used to thicken water by stirring a prescribed amount of clay into the water. The amount of thickening achieved is a direct function of the amount of clay used and the amount of work put into the system by agitation shear. These same clays can be used to thicken organic liquids by pretreating the clays with certain organic surfactants prior to agitating into the liquid, or by adding the clays to the liquid at the same time as the surfactant and accomplishing interaction of the clay and surfactant in situ.
Of the above clays, Wyoming bentonite and hectorite are platy clays that are able to imbibe water and swell to achieve their thickening effect. Swelling is an inherent property of these clay minerals because of the cations (type of cation) between adjacent platelets which are of a type (NA+ for example) that allows them to take up water. When the ionic content of the water is high, they will not imbibe water and thus are not thickeners for salt-containing solutions.
Attapulgite, sepiolite and palygorskite are acicular clay minerals that can be made to thicken water by merely stirring them into the water. Thickening is achieved with these minerals by the individual needles being separated and interacting in an extended gal structure to thicken the continuous water phase. Because of their method of building viscosity, this group of minerals will effectively thicken water solutions containing high ionic concentrations; e.g., saturated NaCl, gypsum, MgSO.sub.4, etc., and are commonly used commercially when contamination with these materials is encountered.
All of these clay minerals can be predispersed in water with a chemical dispersant such as sodium hexametaphosphate sold under the tradename Calgon by Merck, TSPP (tetrasodium pyrophosphate) and certain phosphate glasses, and used as thickeners by reflocculating the clay by either adding a neutralizing agent for the dispersant (salts containing Ca++, Al+++ or other polyvalent cations) or adding enough ionic material to collapse the double layer. Water systems thickened with platy gelling grade minerals such as Wyoming bentonite tend to be unstable when high concentrations of ionic materials or lower concentrations of polyvalent cations are added. Water systems thickened with reflocculated acicular clays not only tend to be more stable but also exhibit a higher gelling efficiency than when the same liquids are thickened with dry (undispersed) clay additions.
Certain montmorillonite type clays that occur in the region of Ochlocknee, Ga. are classified as nonswelling clays because they show little ability to thicken or gel water. This is a result of the ionic types (Al.sup.+3 and some Ca.sup.+2) existing between their plates which do not permit an autogenous imbibing of water or swelling. In fact these clays will not gel water even with high-shear agitation. The clays are mined commercially and are thermally and mechanically processed to produce granular absorbants that are sold as oil and grease absorbants, pet litters, agricultural chemical carriers, etc..